As a cutting insert for a milling cutter, for example, a cutting insert that is described in Patent Literature 1 below is known.
The cutting insert in this document is usually what is called a vertical use type in which a face that is called a side face is a rake face.
In the cutting insert, in order to make it possible to use two side faces whose backs face each other as rake faces, faces through which a mounting hole extends (in general, faces that are called top and bottom faces) are made flat and parallel to each other. Here, “faces . . . are flat and parallel to each other” refer to faces that, when the side faces, which are rake faces, are flat, form an angle of 90 degrees with respect to the side faces.
In addition, in order to provide a clearance angle to one of the top and bottom faces having this form (for example, to a side that becomes a peripheral flank face) (that is, in order to provide clearance at a position where a corner that is opposite to a corner that is used does not interfere with a workpiece), the cutting insert is used by mounting it on a cutter body while the cutting insert is tilted in a direction in which a radial rake becomes blunt.
Further, in order to also provide a clearance angle to a face that becomes a front flank face (side face that is adjacent to the side faces that become rake faces), the top and bottom faces have parallelogram shapes.